Parents of Delhi gang rape victim have 'no room for mercy' for her condemned attackers

The parents of the woman whose brutal bashing and gang rape in New Delhi last year shocked the world say they have no room in their hearts for mercy for her attackers.

Asha Devi and Badrinath Singh have given a rare personal interview to the ABC's 7.30, less than a week after four men were sentenced to death for the crime.

The couple have welcomed the court's sentence but expressed anger that a teenager received a relatively light sentence for his role.

They have described the crushing despair they have felt since losing their 23-year-old daughter, known to the world as Nirbhaya.

"They must be hanged because if they remain in society they will only spread filth," Ms Devi said of the condemned men.

Nirbhaya and a male companion were attacked after they boarded a bus on December 16.

She was gang raped and violated with a metal bar before being dumped naked with her friend on the side of the road.

"A phone call came from Safdarjung Hospital asking me to come over because my daughter had met with an accident," Mr Singh said.

"Not for a minute did I comprehend what that accident really meant."

Nirbhaya was flown to Singapore for emergency treatment but it was too late. Her injuries were so severe that she died there 13 days later.

An investigation quickly led to the arrest of five men and a juvenile, and under pressure the Indian government promised swift justice.

The trial would be held in a fast-track court; instead of years it would take only months.

Mr Singh said he felt repulsed to see the accused men in person during the trial.

"I feel guilty. I think what type of values do they come from?" he said.

"What kind of men are they... in order to fulfil their small lust they ended one life? They even put their own lives on the line.

"There are two kind of flies - one that eats from the side of your plate and flies away, and the other one who drops on your plate, spoils the food and even dies in it. They are these sort of men."

Last week four men - Akshay Thakur, Pawan Gupta, Vinay Sharma and Mukesh Singh - were convicted of rape, murder and the destruction of evidence.

A couple of days later they were given the death penalty. The judge described their crime as a despicable act committed on a defenceless person.

A fifth accused, Ram Singh, escaped justice by hanging himself in jail in March.

"These sort of savages do not deserve anything less than death by hanging," Ms Devi said.

The death sentence sits in contrast to the penalty given to the teenager. He was under-age at the time and will spend less than three years in a boys home as his punishment.

It is a sentence that has angered the family.

"It seems they have tried to lure us with the maximum sentencing of three years, but it's just an eyewash," Ms Devi said.

"There's a saying that the law's ambit is huge, that the legal system has very long hands... then why are its hands falling short in delivering justice? I'd like to ask that."

The crime provoked fury on the streets in New Delhi and started a debate about the way women are treated in India.

More than 20,000 cases of assault and molestation are reported every year. The conviction rate is less than 15 per cent.

And while outrage at the gang rape sparked a debate about the treatment of women, change appears to be happening slowly.

In the nine months since the gang rape, there have been more than 1,000 reported rapes in the Delhi area alone.

Nirbhaya's father says it is unlikely his family will ever fully recover, but he does hope his daughter can leave a legacy - that the violence she endured leads to changes that ultimately makes women safer.

"Not just India, but for the entire world," he said.

"She has become a symbol of women's empowerment. She has lit a flame and we have to keep that flame burning."